Motion picture encoding/decoding apparatus, and method and apparatus for hybrid block motion compensation/overlapped block motion compensation for same

ABSTRACT

A hybrid block motion compensation/adaptive overlapped block motion compensation apparatus for an encoding apparatus includes: a selector for selecting between a block motion compensation BMC and an overlapped block motion compensation OBMC with respect to a current block in units of pixels according to a set criterion; an adaptive motion compensator; a scan mode setter for scanning the current block in a plurality of set scan modes and establishing a scan mode causing a smallest number of transitions between the BMC and OBMC; and an information recorder for recording transition information at locations of the pixels corresponding to the transitions between the BMC and OBMC. A decoding apparatus is disclosed including: an interpreter for scan mode information of a current block and information about transitions between the BMC and OBMC for each of pixels of the current block; and an adaptive motion compensator for operating in units of the pixels.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority of Korean Patent Application No.10-2008-0101131, filed on Oct. 15, 2008, in the KIPO (KoreanIntellectual Property Office), the disclosure of which is incorporatedherein in their entirety by reference. Further, this application is theNational Phase application of International Application No.PCT/KR2009/005744, filed Oct. 8, 2009, which designates the UnitedStates and was published in Korean. Each of these applications is herebyincorporated by reference in their entirety into the presentapplication.

TECHNICAL FIELD

The present disclosure relates to a video data compression/decompressiontechnique. More particularly, the present disclosure relates to a videoencoding/decoding apparatus, and method and apparatus for hybrid blockmotion compensation/overlapped block motion compensation adapted toapply an overlapped block motion compensation (OBMC) by units of a pixelwherein the disclosure removes complex computations needed fordetermining the method of motion compensation with respect to each ofthe pixels to control the computation complexity, performs an optimummotion compensation by units of a pixel so as to generate least residualpixel energy to increase the compression performance in an encoding, andresolves a blurring artifact or an over-smoothing problem inherent inOBMC.

BACKGROUND ART

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Generally, the most currently existing commercial video compressionmethods and their apparatuses effectively remove temporal redundancieswhich are present in natural videos by using a block motionestimation/compensation method and an apparatus thereof. Such a blockmotion estimation/compensation method is based on an assumption that allthe pixels in a block basically have the same motion, and performs aprediction/reconstruction on the respective block pixels of the subjectcurrent image to be encoded by using previously compressed andtransmitted image(s). Propelled by the simple but efficient basicassumption, the block motion compensation has a little motion parametersto encode and transmit, and thereby makes a significant contribution toimproving the compression efficiency of video data. However, this methodinvolves blocking artifacts caused by a lack of conformity that somepixels (normally at block boundaries) in the blocks do not conform to abasic model, wherein the blocking artifact means unsightly latticedartificial coding errors observed at the respective block boundaries. Inorder to solve the blocking artifacts, many conventional techniques havebecome available, and the overlapped block motion compensation is one ofthem.

The technique of overlapped block motion compensation is performed inmotion reconstructions for the respective blocks by a weighted additionof the reconstructed current location pixels based on motions ofadjacent blocks to reconstructed pixels in a current block as a way ofreflecting the motions of the adjacent blocks in the motionreconstruction of the current block, whereby errors in the motionreconstruction at the block boundaries are effectively and significantlyreduced. However, in the case where the motions of the adjacent blockare significantly deviated from the current block, the motionreconstruction by the overlapped block motion compensation is known toshow a greater deterioration than the typical block motionreconstruction or cause blurring artifacts which blur edge informationof the blocks. This phenomenon is often called over-smoothing problem,which occurs when the relatively correctly predicted pixel values at theblock boundaries under the well satisfied assumption with the blockmotion estimation method undergo a weighted addition to pixels in theadjacent blocks having a critical error caused by the overlapped blockmotion reconstruction. Generally, the reason for showing a significantdifference between motions of two adjacent blocks is because the most ofthe pixels in the respective blocks have disparities in actual motionswhich are caused by the different imaged objects of possibly differentdynamic natures within the video. Therefore, such over-smoothing problemgenerally occurs to the in-video objects at their edges which happen tobe extra important video information, and thus resolving theover-smoothing problem is important in further improving the videocompression performance and obtaining an even higher qualityreconstructed video.

To solve such over-smoothing problem, there exist prior arts in the formof various techniques that mostly address the motion reconstruction ofthe respective blocks by adaptively applying, via selecting between, theoverlapped block motion compensation and the typical block motioncompensation. According to Ji Zhongwei, Jiang Wenjun, and Zhu Weile(“Wavelet-based video coding using adaptive overlapped block motioncompensation”, in Proc. ICCCS'02, 29 Jun.-1 Jul. 2002, vol. 2, pp.1090-1093), encoding is performed as the respective blocks are triedwith the overlapped block motion compensation and the conventional blockmotion compensation, and then mean-squared errors for the respectivemethods are compared to select one that has a lower value. Though thistechnique could have attained an improved motion reconstructionperformance by way of time-processing always in a method with lesserrors in motion compensation, a decoder is unable to reproduce themean-squared errors for the respective methods which the encoder used inits selection, necessitating transmission of a form of additionalinformation as to the method for motion-reproducing the respectiveblocks and the consequent bit rate of the information may pointedlydeteriorate the overall compression performance.

There are various types of prior arts to perform an adaptive overlappedblock motion compensation while handling the problematic increase of bitrate with the extra information transmission, and firstly Tien-ying Kuoand C.-C. Jay Kuo (“A hybrid BMC/OBMC motion compensation scheme”, inProc. ICIP'97, 26-29 Oct. 1997, vol. 2, pp. 795-798) suggested to obtaina displaced frame difference from two previously decoded images based onwhich the motion compensation methods were switched. In particular, adecoder with no extra information was made to adaptively select betweenthe block motion compensation and the overlapped block motioncompensation by allowing the overlapped block motion compensation to beperformed only when a differential image block at the same location ofthe current block for being motion compensated has a number of pixelsabove a particular threshold. Likewise, other various conventionaltechniques have their proprietary criteria to obviate extra informationneeded to select the motion compensation methods for each block, andYoung Su Lee suggested in “Moving picture compensation apparatus inMPEG4 decoding”, Korean Patent Registration No. 1002804980000, Nov. 10,2000 to use a high band frequency energy value of transmitted anddecoded DCT (discrete cosine transform) coefficients; Sung-hee Lee andBong-soo Hur (“Apparatus to provide block-based motion compensation andmethod thereof”, US Patent, PN US2004/0252896, Dec. 16, 2004), SeungHwan Kim, Dong-il Chang, Choong Woong Lee, and Sang Uk Lee (“Complexityreduction method for overlapped block motion compensation based onspatio-temporal correlation”, in Proc. ISCAS'99, 30 May-2 June 1999,vol. 4, pp. 211-214), and others suggested using motion vectordifferences between a current block under decoding and its neighboringblocks as the criteria; and Jun Zhang (“Adaptive overlapped blockmatching for accurate motion compensation”, US Patent, PNUS2006/0083310, Apr. 20, 2006) selectively applies an overlapped blockmotion compensation based on the statistical standard deviation betweeninside and outside regions of a block for the motion compensation.

Though the above prior arts for adaptively selecting motion compensationmethods without requiring extra information have contributed torelieving from the over-smoothing problem by providing their respectiveselection criteria, they commonly have one important deficiency. Thatis, the respective approaches select a motion reconstruction method inunits of respective blocks methods and let the selected method appliedto performing motion reconstructions on all of the pixels within ablock, which disables a motion reconstruction in a finer unit such as onthe basis of boundaries of the respective blocks or by each pixel in ablock resulting in incomplete solutions to the over-smoothing problem.

This deficiency may be somewhat resolved by a method suggested by JiroKatto (“Overlapped motion compensation using a window function whichvaries in response to an input picture”, U.S. Pat. No. 5,602,593, Feb.11, 1997) wherein a weight for use in the weighted addition is adjustedby an input image and the statistical characteristics of a motioncompensation error. In other words, the value of the weight for use inthe overlapped block motion compensation is made variable by thestatistical characteristics of a particular video inputted or aparticular image of the inputted video, or even a particular boundary ofthe inputted image with the weight valued ‘0’ directing the typicalblock motion compensation method, which entitles the suggested method tobe an expansion of the conventional block based adaptive motioncompensation method for selecting motion reconstruction methods to aneven more refined level at the block boundary units. However, since thestatistical characteristics referred to in this method as being thebasis for adjusting the weight mean the inputted images, or astatistical standard deviation and correlation belonged to a group ofpixels corresponding to a part of an image, and a statistic expectationof the motion reconstruction errors, there is a significant computationvolume required for their estimations, and its application to such asmall region as a block boundary increases the uncertainty of theestimation accuracy resulting in a limitation of the performance.Besides, such statistical parameters used in the weight adjustment arenot what can be reproduced by calculations in a decoder and they must bedisadvantageously transmitted in the form of extra information to thedecoder.

Problems with the suggested method by Jiro Katto (“Overlapped motioncompensation using a window function which varies in response to aninput picture”, U.S. Pat. No. 5,602,593, Feb. 11, 1997) are expected tobe resolved by a modification of the suggestion of Byeong-Doo Choi,Jong-Woo Han, Chang-Su Kim, and Sung-Jae Ko (“Motion-compensated frameinterpolation using bilateral motion estimation and adaptive overlappedblock motion compensation”, IEEE Trans. Circuits and Syst. for VideoTechnol., vol. 17, pp. 407-416, April 2007) which is based on areliability for indicating the similarity of reconstructions of pixelsof the subject block using motions of boundary blocks to the actualpixels of the block for current reconstruction and uses a greater weightin proportion to the reliability. However, because this method isdesigned for application of frame interpolation, the reliabilityinformation in the video compression application cannot be reproduced ina decoder as the weight adjustment criterion, and the method is unableto expand towards the overlapped block motion compensation by the pixelunits short of becoming a more refined type of the adaptive technique.

An example of a conventional method for adjusting the overlapped blockmotion compensation by the pixel units was suggested by Chih-lung BruceLin, Ming-Chieh Lee, and Wei-ge Chen (“Overlapped motion compensationfor object coding”, U.S. Pat. No. 5,982,438, Nov. 9, 1999) wherein therespective pixels in a single block are subjected to the overlappedblock motion compensation only when they belong to the same object asthat of the adjacent blocks whereby the over-smoothing problem isresolved. However, this method needs a provision of an object map and atransmission as additional information of the object map, which ishardly generated by the current techniques automatically from naturalimages which renders it really impractical for compressed encoding ofvideo information.

DISCLOSURE Technical Problem

Therefore, the present disclosure has been made for providing a videoencoding/decoding apparatus, and method and apparatus for hybrid blockmotion compensation/overlapped block motion compensation which allow forperforming optimum motion compensation for each pixel with the leastcomputation volume or complexity that has been possible. In particular,the present disclosure is to provide a video encoding/decodingapparatus, and method and apparatus for hybrid block motioncompensation/overlapped block motion compensation adapted to apply anoverlapped block motion compensation (OBMC) by units of a pixel whereinthe disclosure removes complex computations needed for determining themethod of motion compensation with respect to each of the pixels tocontrol the computation complexity, performs an optimum motioncompensation by units of a pixel so as to generate least residual pixelenergy to increase the compression performance in an encoding, andresolves a blurring artifact or an over-smoothing problem inherent inOBMC.

Technical Solution

In order to achieve the above objectives, the present disclosureperforms an adaptive pixel overlapped block motion compensation with areduced calculation volume and an optimized selection of motioncompensation for each pixel by using dedicated BMC/OBMC determinationcriteria in an encoder for determining the best motion compensationmethod by pixel units of an image block, and has the encoder assign avery small bit for generating information that can identify the BMC/OBMCdetermination with respect to each pixel of the block, and allows thedecoder to determine the motion compensation method for each pixel byreferring to a very small bit transmitted from the encoder without theneed to reproduce the formula used in the encoder for the best BMC/OBMCdetermination, thereby the decoder can perform the best motioncompensation by pixel units with a small calculation volume.

One aspect of the present disclosure provides a hybrid block motioncompensation/adaptive overlapped block motion compensation apparatusincluding: a BMC/OBMC selector for performing a BMC/OBMC selectionbetween a block motion compensation BMC and an overlapped block motioncompensation OBMC with respect to a current block in units of pixelsaccording to a set criterion; an adaptive motion compensator forperforming a motion compensation after the selection; a scan mode setterfor scanning the current block in a plurality of set scan modes andestablishing a scan mode causing a smallest number of transitionsbetween the BMC and the OBMC; and an information recorder for recordingtransition information at locations of the pixels corresponding to thetransitions between the BMC and the OBMC.

Another aspect of the present disclosure provides a hybrid block motioncompensation/adaptive overlapped block motion compensation methodincluding: performing a BMC/OBMC selection between a block motioncompensation BMC and an overlapped block motion compensation OBMC withrespect to a current block in units of pixels according to a setcriterion; scanning the current block in a plurality of set scan modesand establishing a scan mode causing a smallest number of transitionsbetween the BMC and the OBMC; recording transition information atlocations of the pixels corresponding to the transitions between the BMCand the OBMC; and performing a motion compensation according to theBMC/OBMC selection.

Yet another aspect of the present disclosure provides a video encodingapparatus including: a motion estimator/compensator for performing aselection between a block motion compensation BMC and an overlappedblock motion compensation OBMC with respect to a current block in unitsof pixels, performing a motion compensation after the selection topredict a predicted pixel value of each of the pixels, scanning thecurrent block in a plurality of set scan modes and generating anestablished scan mode causing a smallest number of transitions betweenthe BMC and the OBMC, and recording transition information during thescanning in the established scan mode at locations of the pixelscorresponding to the transitions between the BMC and the OBMC; asubtractor for generating a residual signal by calculating a differenceof the predicted pixel value of each of the pixels of the current blockto an original pixel value of each of the pixels of the current block; atransformer for performing a transform on the residual signal intofrequency coefficients; a quantizer for performing a quantization thefrequency coefficients after the transform; and an encoder for encodingthe frequency coefficients after the quantization into a bitstream.

Yet another aspect of the present disclosure provides a video decodingapparatus including: an information interpreter for performing aninterpretation of information about a scan mode of a current block andinformation with respect to each of pixels of the current block undereither a block motion compensation or an overlapped block motioncompensation about transitions between the block motion compensation andthe overlapped block motion compensation; and an adaptive motioncompensator for operating based on the information about the scan modeand the information about the transitions after the interpretation toperform an adaptive motion compensation in units of the pixels.

Yet another aspect of the present disclosure provides a video decodingmethod including: performing an interpretation of information on a scanmode of a current block; performing an interpreting of information ontransitions between a block motion compensation and an overlapped blockmotion compensation with respect to each of pixels of the current block;and performing an adaptive motion compensation in units of the pixelsbased on the information on a scan mode after the interpretation and theinformation on transitions after the interpretation.

According to the present disclosure, an encoder may include: a BMC/OBMCselector for providing optimum motion compensation selection for each ofthe pixels by using a dedicated criteria or formula; an adaptive motioncompensator for performing a motion compensation based on the motioncompensation selection; a scan mode setter for setting a mode forscanning the current block pixels provided with their motioncompensation selections in a way to minimize transitions from BMC toOBMC and vice versa; and an information recorder that operates duringthe scanning in the set scan mode to record separate transitioninformation for a decoder to use at the pixel location where theBMC/OBMC transition occurs. In addition, a decoder may include aninformation interpreter for interpreting, upon receipt of, informationof the set scan mode from the encoder and information of the recordedBMC/OBMC transition from the encoder to provide the respective currentblock pixels with their motion compensation selections; and an adaptivemotion compensator for performing optimum motion compensation for eachof the pixels based on the interpreted information.

The BMC/OBMC selector starts with performing both the overlapped blockmotion compensation and the block motion compensation with respect toall of the pixels in the respective blocks and determines one of the twoas a motion compensation method of the block which causes less absolutevalue of the residual pixels from between the original image and amotion compensated image. Though this technique may provide an improvedmotion reconstruction performance by way of time-processing always in amethod with less errors in motion compensation, because the decoder isunable to reproduce the selection criteria which the encoder used, thereis a need for a transmission in the form of additional information (thatis, information on scan modes and BMC/OBMC transitions) as to how therespective blocks should be motion-reproduced. For this reason,processing the additional information on the basis of spatialcorrelations of the images enables deterministic information for themotion compensation method with very little bit rate. Specifically,assigning bits exclusively to the pixels where the BMC/OBMC transitionsoccur and taking advantage of various scan modes to reduce the BMC/OBMCtransition regions result in a reduction of information to transmit.

The adaptive motion compensator performs the motion compensationselected in the BMC/OBMC selector. It performs BMC on the pixels underthe BMC selection and OBMC on the pixels under the OBMC selection.

The scan mode setter according to the disclosure applies various modesof scan method with respect to the current block having the BMC/OBMCselections performed pixel by pixel on the basis of their spatialcorrelations to decide a scan mode causing a lowest frequency of theBMC/OBMC transitions. Generally, in a natural image, spatially closerpixels are more probable to have a same motion. Pixels moving in accordare supposed to undergo a same block motion compensation selected andcause infrequent BMC/OBMC transitions as will be revealed from scanningthe entire pixels in a block. Moreover, when various scan modes areapplied reflecting the characteristics of the block, it is possible tofind the scan mode which generates the least BMC/OBCM transitions.

The information recorder of the disclosure records 1-bit information atthe pixel where the BMC/OBMC transition occurs when the scanning isconducted in the set scan mode. Information about what scan mode is usedand information recorded at the pixel experiencing the BMC/OBMCtransition are transmitted to the decoder. Simply recording the scanmode information and the BMC/OBMC transition pixel information meansvery small bit rate is needed to record information for determining themotion compensation method. When this information is received and usedin the decoder, a complex formula used for the BMC/OBMC determination inthe encoder may be avoided advantageously in determining the BMC/OBMC inthe decoding operation.

In addition, the information recorder of the disclosure has toincorporate 1-bit information for telling if the starting pixel of thecurrent block is BMC or OBMC into the BMC/OBMC transition information.Knowing if the BMC or OBMC were applied to the first pixel is necessaryto determine the motion compensation methods for the remaining pixelsbased on the BMC/OBMC transition information.

Based on the transmission of the information on the scan mode and thetransition information recorded at the BMC/OBMC transition pixels, theinformation interpreter of the disclosure interprets whether BMC or OBMCwas assigned with respect to the entire pixels in the current block.Therefore, the decoder of the disclosure can avoid the complex formulaused to make the BMC/OBMC determinations in the encoder in determiningthe same to achieve optimal motion compensation.

According to the disclosure, the adaptive motion compensator of thedecoder operates based on the interpreted information to perform theadaptive motion compensation by pixel units with respect to the entirepixels in the current block. Because the motion compensation used in thedecoder is identical to that in the encoder, errorless optimal motioncompensation may be used.

According to the present disclosure, the encoder may include steps ofoperation of: selecting BMC/OBMC during an encoding from performing boththe BMC and the OBMC with respect to all of the pixels in the respectiveblocks and determining one of the two as a motion compensation method ofthe block which causes less absolute value of the residual pixels;determining a scan mode by first applying various scan modes withrespect to the entire pixels of the current block and determining thescan mode in a way to cause the lowest frequency of the BMC/OBMCtransitions; recording information based on the determined scan mode byrecording information on the BMC/OBMC transitions occurring at thepixels of the current block; and performing an adaptive motioncompensation in units of the pixels on the basis of the selection resultfrom the step of selecting the BMC/OBMC. The information from the stepof recording information on the BMC/OBMC transitions may be transmittedto the decoder for use in determining the BMC/OBMC.

According to the present disclosure, the decoder may include steps ofoperation of: performing an interpretation of information byinterpreting transmitted information from the encoder and determiningthe BMC/OBMC with respect to the entire pixels of the current block; andadaptively performing optimal motion compensation based on theinterpreted information with respect to the entire pixels of the currentblock.

Advantageous Effects

According to the disclosure, the encoder first determines the optimalmotion compensation by pixel units and then generates very little bit ofthe same and transmits it to the decoder which uses this informationreceived but no extra calculation steps to adaptively select the bestmotion compensation by pixel units that the encoder has determined,thereby significantly reducing the residual signal energy to be encodedto much improve the compression performance of the video compressionapparatus and eventually obtain an enhanced video quality for the samebits or amount of information.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing video frames comprising a video and beingused for an inter prediction between different frames;

FIG. 2 is a block diagram of a video encoding apparatus according to anaspect;

FIG. 3 is a block diagram of a hybrid block motion compensation/adaptiveoverlapped block motion compensation apparatus according to an aspect;

FIG. 4 is a block diagram of a video decoding apparatus according to anaspect;

FIG. 5 is a block diagram of a hybrid block motion compensation/adaptiveoverlapped block motion compensation apparatus according to anotheraspect;

FIG. 6 is a flow diagram for illustrating a hybrid block motioncompensation/adaptive overlapped block motion compensation methodaccording to an aspect;

FIG. 7 is a flow diagram for illustrating a hybrid block motioncompensation/adaptive overlapped block motion compensation methodaccording to another aspect;

FIG. 8 is a diagram for showing a weight matrix of H.263 overlappedblock motion reconstruction according to an aspect; and

FIG. 9 is a diagram for showing various scan modes according to anaspect.

MODE FOR INVENTION

Hereinafter, aspects of the present disclosure will be described indetail with reference to the accompanying drawings. In the followingdescription, the same elements will be designated by the same referencenumerals although they are shown in different drawings. Further, in thefollowing description of the present disclosure, a detailed descriptionof known functions and configurations incorporated herein will beomitted when it may make the subject matter of the present disclosurerather unclear. Also, in describing the components of the presentdisclosure, there may be terms used like first, second, A, B, (a), and(b). These are solely for the purpose of differentiating one componentfrom the other but not to imply or suggest the substances, order orsequence of the components. If a component were described as‘connected’, ‘coupled’, or ‘linked’ to another component, they may meanthe components are not only directly ‘connected’, ‘coupled’, or ‘linked’but also are indirectly ‘connected’, ‘coupled’, or ‘linked’ via a thirdcomponent.

Since a video on a screen is composed of as much as thirty frames persecond causing a short inter-frame interval, human eyes cannotdistinguish between the frames. For this reason, casting the thirtyframes within a second will make the observing eyes believe the framesare a continuous movement.

If there is such a similarity between a previous frame and a currentframe, it is possible to make a prediction of a pixel value of one framefrom a known value of a pixel constituting a preceding frame. This kindof prediction is called an inter prediction and is carried out frame toframe.

Such video data encoding and decoding are performed based on thetechnology of motion prediction. Motion prediction is carried out in away of referencing to a past frame on a temporal axis or to both of thepast frame and a future frame. The reference frame is a frame that isused as a reference for encoding or decoding a current frame.Additionally, in the block-based video coding, a still image (frame)forming the video is divided by macroblocks and subblocks whichconstitute the macroblock so that the image is motion-predicted andencoded in units of a block.

Prediction of a next pixel is also possible within a same frame bytaking advantage of the correlations among pixel signals, and is calledan intra prediction inside a frame.

FIG. 1 is a diagram showing video frames comprising a video and beingused for an inter prediction between different frames.

Referring to FIG. 1, video data is consisted of a series of stillimages. These still images are classified by a group of pictures (GOP).One GOP has an I frame 110, P frames 120, and B frames 130. I frame 110is adapted to be encoded by itself without using a reference frame, andP frames 120 and B frames 130 are encoded through performing a motionestimation and a compensation using a reference frame. Especially, Bframes 130 are encoded by forwardly and backwardly (bidirectional)predicting a past frame and a future frame, respectively.

FIG. 2 is a block diagram for showing a video encoding apparatus 200according to an aspect.

Referring to FIG. 2, video encoding apparatus (or called encoder) 200includes a motion estimator/compensator 210, a subtractor 220, atransformer 230, a quantizer 240, and an encoder 250.

Video encoding apparatus 200 may be a personal computer or PC, notebookor laptop computer, personal digital assistant or PDA, portablemultimedia player or PMP, PlayStation Portable or PSP, or mobilecommunication terminal, smart phone or such devices, and represents avariety of apparatuses equipped with, for example, a communicationdevice such as a modem for carrying out communications between variousdevices or wired/wireless communication networks, a memory for storingvarious programs for encoding videos and related data, and amicroprocessor for executing the programs to effect operations andcontrols.

As described above, motion estimator/compensator 210 may predict thecurrent block (or macroblock) by using either one or combined both ofthe motion prediction-based inter prediction and intra prediction forpredicting a latter pixel by taking advantage of the correlations amongthe pixel signals within a single frame.

For example, motion estimator/compensator 210 may be formed by twodivided sections of a motion estimator (not shown) and a motioncompensator (not shown). The motion estimator searches the predictedvalue of a motion of the current frame macroblock from the referenceframe and outputs their motion difference as a motion vector. In otherwords, the desired macroblock to find is searched for within apredetermined search area of the reference frame to identify the closestmacroblock and its degree of motion is outputted as the motion vector.From the reference frame, the motion compensator gets a predictedmacroblock corresponding to the obtained motion vector.

Alternatively, motion estimator/compensator 210 may be an intrapredictor which predicts the current macroblock of the current frame byusing macroblocks neighboring the current block, and it predicts thepredicted macroblock by calculating predicted pixel values of therespective pixels in the current block using one or more pixel values ofone or more adjacent macroblocks. Here, the adjacent macroblocks may beone or more macroblocks which were compressed previously of the currentmacroblock and are neighboring the current macroblock.

Subtractor 220 subtracts the predicted macroblock from the macroblock ofthe original video to calculate their difference for generating residualsignals.

Transformer 230 transforms the residual signals generated by subtractor220 into a frequency domain to obtain frequency coefficients. Here,transformer 230 performs the transform into frequency domain by usingvarious techniques including discrete cosine transform (DCT) or wavelettransform that transforms video signals on the time axis to those of thefrequency axis. In the case of I frame described with reference to FIG.1, transformer 230 transforms the macroblocks of the original video intothe frequency domain.

Quantizer 240 performs quantization on the frequency coefficients thatwent through transformation at transformer 230.

A residual signal refers to the macroblock of the original videosubtracted by the predicted macroblock, and for the purpose of reducingthe data quantity in the encoding operation the value of the residualblock is encoded. Because errors are generated during the quantization,the bitstream of video data carries errors occurred through thetransform and quantization.

Video encoding apparatus 200 may also incorporate an inverse quantizer360 and an inverse transformer 370 to obtain the reference frame.

For the purpose of obtaining the reference frame, the quantized residualsignal is added to the predicted video from motion estimator/compensator210 after going through inverse quantizer 360 and inverse transformer270 and the sum is stored in a reference frame storage unit (not shown).In the case of the I frame, it proceeds through inverse quantizer 360and inverse transformer 370 and is stored in the reference frame storageunit. In other words, assuming the original video is A and the predictedvideo is B, transformer 230 receives an input of the difference A-Bbetween the original video and predicted video to perform the transform.

Encoder 250 encodes the quantized frequency coefficients from quantizer240 into a bitstream. For the encoding, an entropy method may be usedalthough various other unlimited coding techniques are available foruse.

FIG. 3 is a block diagram of a hybrid block motioncompensation/overlapped block motion compensation apparatus according toan aspect which corresponds to motion estimator/compensator 210 in FIG.2 and is referenced by the same number 210.

As illustrated, this aspect of hybrid block motioncompensation/overlapped block motion compensation apparatus 210 includesa BMC/OBMC selector 211, an adaptive motion compensator 212, a scan modesetter 213, and an information recorder 214.

BMC/OBMC selector 211 selects performance of BMC or OBMC by pixel unitusing dedicated preset criteria with respect to the current block.

Adaptive motion compensator 212 performs the optimal compensationfollowing the method selected by BMC/OBMC selector 211.

Scan mode setter 213 performs various scans over the entire pixels inthe block having their optimal motion compensation methods selected byBMC/OBMC selector 211 and then sets the scan mode in which BMC/OBMCtransitions occur the most scarcely.

Information recorder 214 operates when scan mode setter 213 performs thescanning in the set scan mode to record separate transition informationat the pixel location where the BMC/OBMC transition occurs. In addition,information recorder 214 may record and incorporate BMC/OBMC selectioninformation for a starting pixel of the set scan in the current block,that is, information for telling if the starting pixel is BMC or OBMCinto the transition information.

FIG. 4 is a block diagram of a video decoding apparatus according to anaspect.

As illustrated, video decoding apparatus 400 in this aspect is fordecoding the video by predicting the current block of the video usingone or more adjacent blocks of the current block, and includes a decoder410, an inverse quantizer 420, an inverse transformer 430, an adder 440,and a motion estimator/compensator 450.

As with video encoding apparatus 200 described with reference to FIG. 2,video decoding apparatus 400 may be a personal computer or PC, notebookor laptop computer, personal digital assistant or PDA, portablemultimedia player or PMP, PlayStation Portable or PSP, or mobilecommunication terminal, smart phone or such devices, and may represent avariety of apparatuses equipped with, for example, a communicationdevice such as a modem for carrying out communications between variousdevices or wired/wireless communication networks, a memory for storingvarious programs for encoding videos and related data, and amicroprocessor for executing the programs to effect operations andcontrols.

Decoder 410 decodes the bitstream to extract the quantized frequencycoefficients. Specifically, decoder 410 decodes the bitstream which isthe video encoded by video encoding apparatus 200 and extracts thequantized frequency coefficients which contain pixel information of thevideo current block.

Inverse quantizer 420 performs a de-quantization with respect to thefrequency coefficients extracted from the bitstream by decoder 410.

Inverse transformer 430 inversely transforms the de-quantized frequencycoefficients from inverse quantizer 420 into time-domain to generate aresidual signal.

Adder 430 adds predicted pixel values of the respective pixels of thecurrent block predicted by motion estimator/compensator 450 to theinversely transformed residual signal to reconstruct the original pixelvalue of the current block.

FIG. 5 is a block diagram of a hybrid block motioncompensation/overlapped block motion compensation apparatus according toan aspect which corresponds to motion estimator/compensator 450 in FIG.4 and is referenced by the same number 450.

As illustrated, this aspect of a hybrid block motioncompensation/overlapped block motion compensation apparatus 450 includesan information interpreter 451 and an adaptive motion compensator 452.

Based on transmission of the transition information as to the pixellocations where the BMC/OBMC transitions occurred and the scan modeinformation as to what scan mode was used, information interpreter 451interprets whether the motion compensations of the respective pixels inthe current block were done in BMC or OBMC.

Adaptive motion compensator 452 operates based on informationinterpreted by information interpreter 451 (the scan mode informationand BMC/OBMC transition information) to perform the adaptive motioncompensation by pixel units.

FIG. 6 is a flow diagram for illustrating a hybrid block motioncompensation/overlapped block motion compensation method according to anaspect, and will be described as operatively applied to motionestimator/compensator 210 of encoder 200 in FIG. 2 corresponding tohybrid block motion compensation/overlapped block motion compensationapparatus 210 in FIG. 3.

First, BMC/OBMC selector 211 selects performance of BMC or OBMC by pixelunit using dedicated criteria with respect to the current block in stepS610.

Next in step S620, scan mode setter 213 performs various scans over theentire pixels in the block having their motion compensation methodsselected by BMC/OBMC selector 211 and then sets the scan mode in whichBMC/OBMC transitions occur the most scarcely.

Then, information recorder 214 operates at the scanning in the set scanmode to record separate transition information at the pixel locationwhere the BMC/OBMC occurs in step S630.

In the last step S640, adaptive motion compensator 212 performs theoptimal compensation following the method selected by BMC/OBMC selector211.

FIG. 7 is a flow diagram for illustrating a hybrid block motioncompensation/overlapped block motion compensation method according toanother aspect, and will be described as applied to motionestimator/compensator 450 of decoder 400 in FIG. 4 corresponding tohybrid block motion compensation/overlapped block motion compensationapparatus 450 in FIG. 5.

Firstly in step S710, based on a transmission of the transitioninformation on the pixel locations where the BMC/OBMC transitionsoccurred and the scan mode information on the scan mode used,information interpreter 451 interprets whether the motion compensationsof the respective pixels in the current block were done in BMC or OBMC.

Lastly in step S720, adaptive motion compensator 452 operates based onthe interpreted information to perform the adaptive motion compensationby pixel units.

Now, a particular example of the present disclosure will be presented tofacilitate a more specific understanding of the above description.

For the purpose of the specific description, the overlapped block motioncompensation technique of H.263 (“Video coding for low bit ratecommunication”, Draft, ITU-T Recommendation H.263, September 1997) willbe first discussed.

The overlapped block motion compensation by H.263 is accomplished inunits of 8×8 block through a calculation of Equation 1:

$\begin{matrix}{{p\left( {x,y} \right)} = {\left\lbrack {{{q\left( {x,y} \right)} \cdot {H_{C}\left( {x,y} \right)}} + {\sum\limits_{N}{{r_{N}\left( {x,y} \right)} \cdot {H_{N}\left( {x,y} \right)}}} + 4} \right\rbrack/8}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, p(x,y) means a motion compensated pixel value to be generated bythe overlapped block motion compensation, and coordinates (x,y) indicatethe locations of pixels in the 8×8 block and have values 0 to 7 with thetop left location of the block being (0,0). In addition, q(x,y) means amotion compensated pixel value of the 8×8 block subject to the currentreconstruction and it is obtained through Equation 2 if the motionvector received via transmission for the current block (MV_(C) ^(x),MV_(C) ^(y)):q(x,y)=f _(t-1)(x+(MV _(C) ^(x) ,y+MV _(C) ^(y))  [Equation 2]

Here, f_(t-1)(x,y) means the pixel values of the previouslyreconstructed image at locations (x,y).

In Equation 1, N indicates neighboring blocks of the block subject to acurrent reconstruction and is valued T, B, L, or R representing indicesof blocks neighboring the current block at its top, bottom, left, andright boundaries, respectively. Therefore, when N=T is given, r_(N)(x,y)is obtained as with r_(T)(x,y)=f_(t-1)(x+(MV_(T) ^(x), y+MV_(T) ^(y)),where (MV_(T) ^(x), MV_(T) ^(y))| means a motion vector received viatransmission for the top adjacent block to the current block. Similarly,for other values of N, it is also possible to obtain r_(N)(x,y) by usingmotion vectors of the neighboring blocks and the previouslyreconstructed image. Finally, in Equation 1, H_(C)(x,y) and H_(N)(x,y)represent weights located at (x,y) and multiplied by q(x,y), a block ofpixels reconstructed into the motion vector of the current block and byr_(N)(x,y), a block of pixels reconstructed into the motion vector ofthe neighboring block, the weight matrix by the respective locationsbeing illustrated in FIG. 8.

As described above, the overlapped block motion compensation method byH.263 uses the statistically optimized fixed weight matrix to performmotion compensations for every 8×8 block via Equation 1 and therebynoticeably reduces the block effect relatively to its prior art blockmotion compensations. However, the reconstructed image will have partialblocks that generate significantly degraded residual signals compared tothe prior art block motion compensations, and the conventionaltechniques as above merely amount to setting the respectivelyproprietary criteria for identifying such partial blocks. Further, evenwith the blocks through the overlapped block motion compensation whichmay seem to be excellent over those through the block motioncompensation, it is visible that not all of the neighboring boundaryblocks positively affect the results of the overlapped block motioncompensation, which suggests the necessity of an adaptive application ofthe overlapped block motion compensation by units of block boundary notof block or by more refined units of pixel for the purpose of theperformance enhancement. However, the application of the overlappedblock motion compensation in the pixel level needs the determination ofwhether to have all of the pixels constituting the image go through theoverlapped block motion compensation, which entails complexcomputations. Particularly, the implementations of the decoder by PC,notebook or laptop computer, PDA, PMP, PlayStation Portable or PSP, ormobile communication terminal have a limited operation capacity and getinto troubles with their implementations in the case of a highcomputational complexity on the decoder and thus reducing the decodercomputing complexity is critical.

In order to solve this problem, the present disclosure provides a methodand an apparatus for performing optimal overlapped block motioncompensation by pixel units without an extra complex computation.

In FIG. 3, to determine optimal overlapped block motion compensationmethods for all of the pixels of the current block, BMC/OBMC selector211 compares the absolute values of residual pixels from the BMC wayconducted on every one of the pixels in the current blocks against thosefrom the OBMC way on the same pixels and identifies the blocks after themotion compensation in such ways that generated the lower absolutevalues of the residual pixels.

When the pixel values in a block of an image under encoding are definedf_(t)(x,y), the pixels after a block-motion-reconstruction by usingmotion vectors of the current block are defined f_(C)(x,y), and themotion compensated pixels to be generated by an overlapped block motioncompensation in consideration of adjacent blocks are p(x,y), theresidual signals R_(BMC)(x,y) with the block motion compensation appliedand the residual signals R_(OBMC)(x,y) with the overlapped block motioncompensation applied may be expressed as Equation 3 and Equation 4,respectively.

The calculated R_(BMC)(x,y) from Equation 3 and R_(OBMC)(x,y) fromEquation 4 are used to check for satisfaction of Equation 5 and if yes,the pixels at location (x, y) are made to generate through BMC, andotherwise, through OBMC. In this way, since the motion compensation isperformed generating less residual pixels, which enhances the encodingperformance.

Being an aspect of the present disclosure, the criterion applied in theabove description may be replaced by any other BMC/OBMC determiningcriteria with the scope of the instant disclosure.R _(BMC)(x,y)=f _(t)(x,y)−f _(C)(x,y)  [Equation 3]R _(OBMC)(x,y)=f _(t)(x,y)−p(x,y)  [Equation 4]|R _(BMC)(x,y)|≦|R _(OBMC)(x,y)|  [Equation 5]

In FIG. 3, scan mode setter 213 operates on the entire pixels in thecurrent block and scans them in diverse directions to determine scanmodes in ways to cause transitions from OBMC to BMC and vice versa.

Adjacent pixels in the block may have a high probability of shaping asame object in an image so that they have a common motion. This leads toa high probability that the pixels adjacent to the current block use asame motion compensation method. In addition, since a block may containdifferent objects having a common motion at various locations, orientingthe scan to have the pixels of the same object expressed in series willcause very little BMC/OBMC transitions enabling expression of the motioncompensation by each pixel requiring very small bite rate.

FIG. 9 is various exemplary scan modes applicable by the presentdisclosure, wherein the diverse scan directions match with the locationsof objects within a block so that BMC/OBMC transitional spots areminimized.

Eight scan modes in FIG. 9 are merely an example of the disclosure andother different scan modes may be used with the scope of the presentdisclosure.

Although increasing the modes of scan may bring a better chance to havethe scan method of getting less BMC/OBMC transitions and save bitscorrespondingly, bits for assigning the scan modes will increase. Ifthere are ‘n’ preset scan modes, the assigning bits are required by thenumber of log₂ n. Within the scope of the present disclosure is a methodfor determining BMC/OBMC for the entire pixels in a block with theminimum possible bit assignments by establishing the best compromiserelationship.

In FIG. 3, information recorder 214 operates when reading pixels valuesin the above scan modes to assign 1-bit information on the locationwhere the BMC/OBMC transitions occur.

During the decoding operation of decoder 400 in FIG. 4, informationinterpreter 451 in FIG. 5 interprets scan mode information on theperformed mode of scanning and the 1-bit information assigned to thepixel where BMC/OBMC transition occurs, and then adaptive motioncompensator 452 may determine between BMC and OBMC to perform andaccomplish the optimal motion compensation.

In the description above, although the components of the embodiments ofthe present disclosure may have been explained as assembled oroperatively connected as a unit, the present disclosure is not intendedto limit itself to such embodiments. Rather, within the objective scopeof the present disclosure, the respective components may be selectivelyand operatively combined in any numbers. Every one of the components maybe also implemented by itself in hardware while the respective ones canbe combined in part or as a whole selectively and implemented in acomputer program having program modules for executing functions of thehardware equivalents. Codes or code segments to constitute such aprogram may be easily deduced by a person skilled in the art. Thecomputer program may be stored in computer readable media, which inoperation can realize the embodiments of the present disclosure. As thecomputer readable media, the candidates include magnetic recordingmedia, optical recording media, and carrier wave media.

In addition, terms like ‘include’, ‘comprise’, and ‘have’ should beinterpreted in default as inclusive or open rather than exclusive orclosed unless expressly defined to the contrary. All the terms that aretechnical, scientific or otherwise agree with the meanings as understoodby a person skilled in the art unless defined to the contrary. Commonterms as found in dictionaries should be interpreted in the context ofthe related technical writings not too ideally or impractically unlessthe present disclosure expressly defines them so.

Although exemplary embodiments of the present disclosure have beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from essential characteristics of thedisclosure. Therefore, exemplary embodiments of the present disclosurehave not been described for limiting purposes. Accordingly, the scope ofthe disclosure is not to be limited by the above embodiments but by theclaims and the equivalents thereof.

INDUSTRIAL APPLICABILITY

As described above, the present disclosure is highly useful forapplication to video encoding/decoding techniques to allow the optimizedmotion compensation method by pixel units to be adaptively selectedwithout needing a complex computation to greatly reduce the residualsignal energy of the block to be encoded to enhance the compressionperformance of the video compression apparatus significantly, andeventually generates improved video quality for the bits (or informationquantity) used.

The invention claimed is:
 1. A hybrid block motion compensation/adaptiveoverlapped block motion compensation (BMC/OBMC) apparatus comprising: aBMC/OBMC selector configured to perform a pixel-by-pixel selection ofone of a block motion compensation (BMC) and an overlapped block motioncompensation (OBMC) with respect to each pixel of a current blockaccording to a preset criterion; an adaptive motion compensatorconfigured to perform a motion compensation according to the selectedone of the BMC and the OBMC; a scan mode setter configured to scan thecurrent block in a plurality of scan modes and establish a scan modecausing a smallest number of transitions between the BMC and the OBMCwith respective to each pixel of the current block in the course of thescanning with respect to the established scan mode; and an informationrecorder configured to record transition information at locations ofpixels corresponding to the transitions between the BMC and the OBMCwith respective to the established scan mode.
 2. The apparatus of claim1, wherein the BMC/OBMC selector is configured to compare, with respectto each pixel of the current block, an absolute value of one residualpixel through performing the BMC with another absolute value of anotherresidual pixel through performing the OBMC to thereby elect a motioncompensation method with a smaller absolute value of a residual pixelbetween the absolute value of the one residual pixel through the BMC andthe another absolute value of another residual pixel through the OBMC.3. The apparatus of claim 1, wherein the information recorder isconfigured to record information on the selected one of the BMC and theOBMC with respect to a starting pixel of the scanning over the currentblock.
 4. A hybrid block motion compensation/adaptive overlapped blockmotion compensation (BMC/OBMC) method performed by a hybrid BMC/OBMCapparatus, the method comprising: performing a pixel-by-pixel selectionof one of a block motion compensation (BMC) and an overlapped blockmotion compensation (OBMC) with respect to each pixel of a current blockaccording to a preset criterion; scanning the current block in aplurality of set scan modes and establishing a scan mode causing asmallest number of transitions between the BMC and the OBMC in thecourse of the scanning with respective to each pixel of the currentblock; recording transition information at locations of the pixelscorresponding to the transitions between the BMC and the OBMC withrespective to the established scan mode; and performing a motioncompensation according to the selected one of the BMC and the OBMC. 5.The method of claim 4, wherein the preset criterion of the selecting oneis to make comparison with respect to each pixel of the current blockbetween an absolute value of one residual pixel through performing theBMC and another absolute value of another residual pixel throughperforming the OBMC to thereby elect a motion compensation method with asmaller absolute value of a residual pixel between the absolute value ofthe one residual pixel through the BMC and the another absolute value ofanother residual pixel through the OBMC.
 6. The method of claim 4,wherein the recording the transition information records information onthe selected one of the BMC and the OBMC with respect to a startingpixel of the scanning over the current block.
 7. A video encodingapparatus comprising: a motion estimator/compensator configured toperform a pixel-by-pixel selection of one of a block motion compensation(BMC) and an overlapped block motion compensation (OBMC) with respect toeach pixel of a current block, perform a motion compensation accordingto the selected one of the BMC and the OBMC to predict a predicted pixelvalue with respective to each pixel of the current block, scan thecurrent block in a plurality of scan modes and generate an establishedscan mode causing a smallest number of transitions between the BMC andthe OBMC in the course of the scanning with respective to each pixel ofthe current block, and record information on the transitions in thecourse of the scanning in the established scan mode at locations ofpixels corresponding to the transitions between the BMC and the OBMCwith respective to the established scan mode; a subtractor configured togenerate a residual signal by calculating a difference of the predictedpixel value of each pixel of the current block to an original pixelvalue of each pixel of the current block; a transformer configured toperform a transform on the residual signal into frequency coefficients;a quantizer configured to perform a quantization the frequencycoefficients after the transform; and an encoder configured to encodethe frequency coefficients after the quantization into a bitstream. 8.The video encoding apparatus of claim 7, wherein the motionestimator/compensator is configured to make comparison with respect toeach pixel of the current block between an absolute value of oneresidual pixel through performing the BMC and another absolute value ofanother residual pixel through performing the OBMC to thereby elect amotion compensation method with a smaller absolute value of a residualpixel between the absolute value of the one residual pixel through theBMC and the another absolute value of another residual pixel through theOBMC.
 9. The video encoding apparatus of claim 7, wherein the motionestimator/compensator is configured to record information on theselected one of the BMC and the OBMC with respect to a starting pixel ofthe scanning over the current block.
 10. A video decoding apparatuscomprising: an information interpreter configured to interpretinginformation on a scan mode of a current block and information ontransitions between a block motion compensation (BMC) or an overlappedblock motion compensation (OBMC) in the course of pixel-by-pixelscanning with respective to each pixel of the current block based on theinterpreted information on the scan mode; and an adaptive motioncompensator configured to perform pixel-by-pixel adaptive motioncompensation with respective to each pixel of the current block based onthe interpreted information about the transitions.
 11. The videodecoding apparatus of claim 10, wherein the interpreted informationabout the scan mode is provided by a video encoding apparatus forperforming an adaptive motion compensation through selecting one fromthe BMC and the OBMC with respect to each pixel of the current block,and scanning the current block in a plurality of scan modes andestablishing a scan mode causing a smallest number of transitionsbetween the BMC and the OBMC.
 12. The video decoding apparatus of claim11, wherein the information about the transitions is recorded during thescanning in the scan mode at locations of pixels corresponding to thetransitions between the BMC and the OBMC.
 13. The video decodingapparatus of claim 11, wherein the interpreted information about thetransitions includes information on the selected one of the BMC and theOBMC with respect to a starting pixel of the scanning over the currentblock.
 14. A video decoding method performed by a video decodingapparatus, comprising: interpreting information on a scan mode of acurrent block; interpreting information on transitions between a blockmotion compensation (BMC) and an overlapped block motion compensation(OBMC) in the course of pixel-by-pixel scanning with respect to eachpixel of the current block based on the interpreted scan mode; andperforming a pixel-by-pixel adaptive motion compensation with respectiveto each pixel of the current block based on the interpreted informationon the transitions between the BMC and the OBMC in the course of thescanning.
 15. The video decoding method of claim 14, wherein theinterpreted information about the scan mode is provided by a videoencoding apparatus for performing an adaptive motion compensationthrough selecting one from the BMC and the OBMC with respect to eachpixel of the current block, and scanning the current block in aplurality of scan modes and establishing a scan mode causing a smallestnumber of transitions between the BMC and the OBMC.
 16. The videodecoding method of claim 15, wherein the interpreted information aboutthe transitions is recorded during the scanning in the scan mode atlocations of pixels corresponding to the transitions between the BMC andthe OBMC.
 17. The video decoding method of claim 15, wherein theinterpreted information about the transitions includes information onthe selected one of the BMC and the OBMC with respect to a startingpixel of the scanning over the current block.